Why is swimming still tied to the fitness skill?

I don't understand why they didn't make these two skills separate especially when Island living came out.

The only thing I can think of is because swimming is a workout I guess but I wish they had the swimming skill separate and your sims have to learn to swim or they have a chance of drowning. Like they have an interaction "try to swim" and it will build up the skill but they have a chance of drowning. And sims can ask for a mentor and parents can teach their kids to swim. And they can also take swimming lessons at university (that's what I did lol).

But yeah it just bothers me a lot that this skill is not separate and I hope they change this in the future.